Automatic circuit breaker having a combined latch and contact unit pivoted to a contact carrier



Dec. 15, 1964 T. M. COLE 3,161,747

AUTOMATIC CIRCUIT BREAKER HAVING A COMBINED LATCH AND CONTACT UNITPIVOTED TO A CONTACT CARRIER Filed July 10, 1961 FIG.3

INVENTQR. THOMAS M. COLE ATTORNEY United States Patent 3,161,747AUTOMATIC CIRCUIT BREAKER HAVING A. CQM- BINED LATCH AND CONTACT UNITPIVOTED TO A CONTACT CARRIER Thomas M. Cole, Harrison, N.Y., assignor toFederal Pacific Electric Company, a corporation of Delaware Filed July10, 1%1, Ser. No. 122,822 11 Claims. (Cl. '200--116) The presentinvention relates to circuit breakers having self-containedoverload-release means.

An object of this invention resides in providing improvements in awell-known type of circuit breaker mechanism having a pivoted cont-actarm on a fixed pivot, an overload-release latch carried by the contactarm and a normally latched pivoted actuator, with a view to increasedsensitivity, improved thermal and magnetic tripping, and reduction incost. Certain features of the invention will be recognized as havingbroader application but, because the invention has particular merit inrelation to this type of circuit breaker, it is disclosed in thatconnection.

As will be seen from the detailed description below, the illustrativeembodiment of the invention is of the type having an enclosing case ofmolded insulation containing a pivoted contact arm, an actuator pivotedto one end of the arm and a contact-and-latch unit pivoted to theopposite end. The pivoted unit has a movable contact that cooperateswith a companion contact when the circuit breaker is closed. The pivotedcontact-and-latch unit and the arm or carrier have a relationshipbetween them, established by contacting parts of each, that locates thelatch for engagement by the actuator. In the embodiment shown, the latchis a current-carrying bimetal, and the thermal calibration isestablished by adjusting the configuration of the carrier, the bimetallatch and the latched actuator. This relationship almost entirelycontrols the overload time-delay tripping level. With this arrangementthe carrier which is a relatively large part can be of inexpensive sheetmetal, rather than of copper or copper alloy used in correspondingprior-ant circuit breakers. This sub-assembly is calibrated by a bendingoperation before it is assembled to the remainder of the circuit breakerparts and completed in its molded casing.

The contact-and-bimetal-latch unit is pivoted into its calibratedattitude in relation to the actuator during opening operation of themoving contact by the opening spring. It is this spring which alsobiases the handle toward its open position.

The two illustrative embodiments described below also include ashort-circuit magnetic tripping mechanism that cooperates with thepivoted latch-and-contact unit. Because the pivoted latch incorporatesthe bimetal, the tripping electromagnet is only required to overcomelatch friction for releasing the breaker. This means that there is noneed for the electromagnet to bend the overcurrent bimetal, in effectingmagnetic tripping. For low-rated circuit-breakers this may be important.Only a small coil will effect almost instant tripping magnetically atrelatively modest short-circuit current. Magnetic tripping in suchbreakers usually is desired at ten times the thermal or delay trippinglevel. It becomes important, in breakers calibrated (for example) forampere thermal tripping, to effect magnetic tripping at only 150 amperesusing an internal tripping coil of minimum size and minimum seriesimpedance in the protected circuit. This performance is achieved due tothe pivoted bimetaland-contact construction in the disclosed embodimentswithout resort to additional separate complicating auxiliary latcharrangements. A further feature, in this connection, is thepre-calibration of the magnetic tripping sensitivity of each circuitbreaker using a bending ICC operation and without, therefore,necessitating adjustment screws and the like. Notably, both magnetic andthermal calibration may be effected without the second adjustmentupsetting the first.

The nature of the invention, and its various advantages, objects andfeatures will be more fully appreciated from consideration of the twoillustrative embodiments shown in the accompanying drawings anddescribed in detail below. In the drawings:

FIG. 1 is a side elevation of an illustrative embodiment of theinvention, with one side wall of the casing removed to reveal theinternal mechanism;

FIG. 2 is an enlarged view of a portion of the circuit breaker in FIG.1, partly in cross-section, with the contacts closed;

FIG. 3 is a fragmentary cross-section of the mechanism in FIG. 2,further enlarged, as viewed from the plane 33 of FIG. 2;

FIG. 4- is an enlarged cross-section of a portion of the circuit breakerin FIG. 1 as viewed from the line 4-4; and

FIG. 5 is another embodiment of the invention viewed as in FIG. 1.

Referring now to the embodiment in FIGS. 1 to 4, a circuit breaker isshown having a rear casing wall 10, a front casing wall 12 (FIG. 4) anda pair of terminals 14 and 16. A moving contact arm or carrier 18 issupported between its ends on a pivot spring 20. An operating handle 22having a pivot 22a has bearings (not shown) in the opposite casingwalls. Handle 22 is connected by a rigid U-shaped wire link 24 to aso-called bell-crank or pivoted actuator 26 that has an insulatedbearing (not shown) at the right-hand end of contact arm 18. Acontact-opening spring 28 acts downward against a portion of contact arm18 to the lefit of pivot 20 as seen in FIG. 1, thereby applyingcounterclockwise bias to the contact arm 18. Spring 23 also appliesclockwise bias to handle 22, both in the open position illustrated andin its closed position at the left-hand extreme position allowed by thecasing. Spring 28 thus applies sustained bias to handle 22 and contactarm 18 urging them in their respective oil or open positions. Adepending portion 18a of the contact arm has an integral extrusion orpivot 1812 that supports contact element 36 of copper having a contactportion 30a of sintered silver-tungsten. Contact portion 30a cooperateswith a corresponding sintered silver-tungsten contact 14a carried by thewireconnecting terminal 14. Contact portions 14a and 30a cooperate in aregion of the casing which forms an arc chamber and has a vent 32 to theexterior.

A current-responsive bimetal 34 is joined by a rivet 3612 (which extendsintegrally from element 30) so that bimetal 34 and contact element 3%form a unit that is pivotally supported by contact arm IS. A stop Illaprojects from the rear casing wall so as to underlie bimetal 34.

Another depending portion of the contact arm carries a coil 36 offlexible copper braid joined to bimetal 3 5 near the right handextremity of the bimetal, the braid having an extension 38 that isunited to plug-in terminal 16 of the circuit breaker. Coil 36 is formedabout a coil form 4d of insulation, and the successive turns of thebraid are separated from each other by insulation on the braid itself oras ribs (not shown) on coil form 40. The coil form fits tightly on core42 of magnetic material riveted to contact-arm portion 180. The axiallength of core 42 is sli htly less than that of the coil form 4-0, sothat there is no danger of electrical contact being made between bimetal34 and core 42. Contact arm 18 is formed of magnetic material such assheet iron, and has an car 18:! extending perpendicular to the plane ofthe drawing (FIGS. 1 and 2), so that a magnetic circuit is formedincluding core 42, and contactarm portions 18c and 18d that is closelycoupled to bimetal 34. The bimetal is of magnetic material, and acts asan armature attracted toward coil 36 when the latter is energized; and asupplemental magnetic part may be added to bimetal 34- if desired.

In the open condition of the circuit breaker, the parts appear asillustrated in FIG. 1. Contact arm 18 is biased counterclockwise byspring 23. An integral car He of the contact arm presses downwardagainst contact element 3d, with the result that spring 2% drivescontact arm 18 and contact element 30 as a unit until bimetal 34 strikescasing projection or stop 10a. This stop limits counterclockwisemovement of contact arm 18, and it also provides counterclockwise biasfor unit 30-34 about pivot 18b. This insures engagement of the pivotedunit 30, 34 with portion 18c of the carrier 18, and locates theright-hand end of the bimetal 34 for latching engagement with the lowerend of actuator 26.

In order to close the circuit breaker, operating handle 22 is movedcounterclockwise about its pivot to apply thrust to link 24 and in thatway to bias actuator 26 clockwise, into latched engagement with bimetal34. Further operating effort applied to the handle drives contact arm13, actuator 25, bimetal 34, and contact element St) clockwise as a unitabout pivot 20. Handle 22 and link 24 constitute two links of anoperating toggle. When this toggle approaches its fully extendedcondition, contact portions 30a and 14a engage. Further effort appliedto the handle 22 builds up contact pressure, forcing pivot spring 20 toflex downward (FIG. 4) and thus building up contact pressure. Theoperating toggle moves somewhat overcenter and locks the circuit breakermechanism with the contacts closed when the projecting portion 221) ofthe handle reaches the left-hand or closed extremity of its strokepermitted by the casing. During the contact-closing operation of themechanism, bimetal 34 lifts away from casing projection 10a; but bimetal34 is arrested by latch friction so as to remain in the triangularconfiguration 18-2644 shown in FIG. 2.

Theparts in the configuration represented in FIG. 2 involve a strongupward pressure of contact portion 39a against contact portion 14a,developed by spring 20 as previously described. The contact face ofcontact 14a is flat, as shown, and the upper surface of contact portion30a is upwardly convex. The plane that is tangent to the point ofengagement between contact portions 14a and 30a coincides with the faceof contact 14a in the construction shown. This plane is perpendicular tothe plane that contains both the axis of pivot 18b and the point ofcontact engagement. Because of the rightangled relationship betweenthese planes, the pressure at the contacts develops neither clockwisenor counterclockwise torque of contact element 39 about pivot 18b. Bylike token, endwise pressure of actuator 26 against bimetal 34 isarranged to provide direct thrust along the length of the bimetalthrough the axis of pivot 18b. Because of this arrangement, thrust alongbimetal 34 does not produce any torque that biases bimetal 34counterclockwise (which would tend to hold it in the latchedconfiguration shown) nor does actuator 26 produce any clockwise torquethat might tend to deflect bimetal 34 in the releasing direction. Themechanism in its closed condition as illustrated in FIG. 2 is thusentirely stable mechanically. The only significant force acting on theunit 30, 34 tending to hold it latched against clockwise movement aboutpivot 18b in response to a magnetic deflecting force is the latchfriction at the latched end of the bimetal.

Current through the circuit breaker flows from terminal 14 throughcontact portions 14a and 3tla, through contact element 30 and bimetal34, through coil 36 and flexible lead 38 to terminal 16. In the event ofa moderate current excess, bimetal 34 heats gradually. The left-hand endof bimetal 34 is fixed in position by pivot 18b and stop 1842. Heatingof the bimetal causes it to deflect downward until it is clear ofactuator 26. When this occurs, springs 20 and 28 are free to restore theparts to the configuration in FIGS. 1 and 4.

The bimetal effects thermal release of the circuit breaker, respondingto persistent but moderate overload currents. Moderate overload currentsof short duration such as are caused during the starting of a motor orduring the in-rush current of an incandescent lamp do not effect thermalrelease of the circuit breaker. However, in the event of a severe,sudden overload current (even if only of short duration) release iseffected by electromagnetic means including coil 36, core 42, andcontact-arm portions 18c and 18d which attract the bimetal downward. Theavoidance of any net mechanical torque acting on bimetal-and-contactunit 30, 34 minimizes the tripping torque required of the electromagnet.Reset of unit 36, 34 by stop a rather than by a spring contributes tothis result. For this reason, the electromagnet which attracts bimetal34 need be of relatively modest strength.

It acts on a long lever arm close to the latching point and effectsrelease merely by overcoming the latch friction between actuator 26 andbimetal 34.

It has been found that the mechanism shown provides a high order ofmagnetic tripping sensitivity. A practical embodiment of the circuitbreaker illustrated has tripped magnetically in response to aninstantaneous current of 150 amperes, using a coil of only three turnson a relatively small core of ordinary sofit iron. The mechanism in FIG.1 is thus an eminently successful circuit breaker that may be adjustedto provide a nominal IS-amperc rating determined by thermal-releaseadjustment, and with a ISO-ampere magnetic tripping adjustment. Wherebimetals of higher ratings are used it is apparent that the coil may bemade smaller and omitted entirely, the bimetal itself then acting as aflux source to cooperate with the magnetic structure below bimetal 34and thus effect magnetic tripping without dependence upon a coil assuch.

Contact arm 18 includes a pair of slots 18 and 18g. When the circuitbreaker is closed as in FIG. 2, a taper pin may be driven progressivelyinto slot 18], gradually reducing the gap between bimetal 34 and themagnetic circuit 4218c18d. Momentary bursts of current of-magnetic-tripping level can be passed through the coil at intervals,while maintaining normal latch pressure. When the gap is reduced to theproper size by this adjustment, the latch will trip. Subsequently, thelatch is engaged again and current of the proper thermal calibrationlevel is passed through it for the required time interval. A taper pinis driven into slot 18g to spread the edges of that slot and therebydecrease the amount of overlap of actuator 26 across the end of bimetal34 until release occurs.

Slots 187 and 18g thus provide independent magnetic and thermaloverload-release adjustments without resort to complicatingadjustment-screw mechanisms. As a matter of practice, these adjustmentsare effected at a time prior to the assembly of the parts of FIG. 2 inan insulating housing, using appropriate fixtures for this purpose.Thereafter, when the circuit breaker is assembled into its housing, nofurther calibrating operations are needed.

A modification is shown in FIG. 5. A modified electromagnet is shownmounted in the bottom of the case 10; Electromagnet 36 is spaced farfrom bimetal 34' when the circuit breaker is open as shown in FIG. 5;but when the circuit breaker is closed, bimetal 34 moves within ashort-gap distance from the electromagnet 36. Casing portion 10a forms astop that engages bimetal 34 and biases [the bimetal against stopportion 18c prior to contact-closing operation of the mechanism. The

embodiment of FIG. 5 has the advantage of reduced mass of parts whichmust move to break the circuit in response to an overload current,thereby effecting some 1 what faster contact-opening operation than theembodiment of FIG. 1. This advantage becomes particularly significantwhere circuit breakers of very high magnetic sensitivity are needed,that is, where magnetic response to low values of current may bedesired. Larger coils may be mounted as in FIG. 5 without concern overthe mass and inertia effects involved. It will be appreciated that thecore in electromagnet 36 may be U-shaped in the embodiment of FIG. 5 ifstill higher magnetic sensitivity is needed or desired.

In both of the embodiments in FIGS. 1 and 5, spring 20 which is stressedin the closed condition of the circuit breaker exerts counterclockwisebias on carrier 18 about the pivot of actuator 26, this being inmechanically arrested position when the circuit breaker is latchedclosed by the toggle actuator 22, 24. The counterclockwise bias ofspring 20 develops contact pressure, this bias being considerablygreater than the relatively softer elfort of spring 28. The latterspring is a push-off spring which biases carrier 18 and the movablecontact 30 counterclockwise and effects contact-opening when actuator 26is released.

Comparable springs are found in circuit breakers of the general formillustrated in which a bimetal and a pivoted actuator latched by thebimetal are carried on a pivotaliy supported contact carrier. In thesecircuit breakers, an operating toggle drives the actuator against thebirnetal and then drives the three elements as a unit (including thebimetal, the pivoted contact arm and the actuator) for driving themovable contact against a companion contact. In the present instance,however, contact-andlaitch unit 30, 34 is pivoted to the carrier.Notably, there is no torque from such springs that acts between carrier18 and unit 30, 34.

- In the closed condition of the circuit breaker illustrated inFIGS. land 5 (as well as in similar prior art circuit breakers wherein themoving contact is fixed to the pivoted contact carrier) link 24 appliesthrust to actuator 26 in the closed condition of the breaker. Thisthrust has a clockwise component biasing the lower end of the actuatoragainst the active end of bimetal latch 34. This biasing component isderived largely from spring 20. The tripping force at the latch end ofbimetal 34 required to overcome the latch friction and the friction atcontacts 14a, 30a may amount to little more than an ounce in a practicaldevice. The contact pressure derived from the same spring 20 in thatpractical device is approximately 20 times as great. It should beunderstood however that various other spring arrangements for developingcontact pressure and latch engagement are known in circuit breakers ofthe type illustrated which may be utilized in place of the particularspring complement shown.

To minimize friction at the contacts as a factor in determination of themagnetic tripping sensitivity, the radius from the contact point ofelements 14a, 39a to the axis of pivot 18b should be minimized. Thebimetal latch 34 in the form illustrated is about five times as long asthe radius of the contacts.

The foregoing specific embodiments of the invention in its variousaspects are presently preferred, but it will be apparent that thefeatures of the invention may be utilized in different applications andin modified forms. Therefore, it is appropriate that the inventionshould be broadly construed in accordance with its full spirit andscope.

What I claim is:

l. A circuit breaker including a movable contact and a companioncontact, a contact carrier movable between open and closed positions, anactuator pivoted to said contact carrier, an overcurrent latch for saidactuator pivoted to said contact carrier, operating means for saidactuator, said carrier, said latch, and said movable contact, andresilient means for providing contact pressure, said movable contactbeing fixed to said latch, and the pressure of said companion contactagainst said movable contact being directed along a line extendingsubstantially from the pivotal axis of said latch.

2. A circuit breaker including a pivoted contact carrier, an actuatorpivoted to the carrier, 2. combined contact-and-latch unit pivoted tosaid carrier and including a movable contact and further including anovercurrent latch co-operable with said actuator, a companion contactengageable by said movable contact, an opening spring acting on saidcarrier for driving the carrier and the movable contact therewith in thecontact-opening direction, a stop for said combined unit interposed inthe opening path thereof and arranged to drive said unit pivotallyagainst a portion of said carrier, thereby to establish a resetrelationship between said latch and said pivoted actuator, a pivotedhandle and a drive connection from said handle to said actuator fordriving the actuator into engagement with said latch in said resetrelationship and thereafter for driving the actuator, the carrier, andthe contact-and-latch unit in the contact closing direction, said handleand said connection constituting a toggle that is erect when thecontacts are closed.

3. A circuit breaker including an enclosing casing of insulation, amovable contact and a companion contact, an elongated carrier for saidmovable contact, a pivot in the casing supporting said contact-carrierbetween the ends thereof, an actuator pivoted to one end of thecontactcarrier, overload release means including a latch normallylatching said actuator when the circuit breaker is closed, a drivingtoggle articulated to said actuator and including an operating handlefor driving and locking the contactcarrier closed, and an opening springbiasing said contact-carrier open, said movable contact and said latchbeing united and being pivoted as a unit to said carrier, and saidcalrier and said unit having co-operating stop portions for arrestingsaid latch in a reset position in the path of said actuator, and meansbiasing said stop portions into cooperation at least when said circuitbreaker is lopen 4. A circuit breaker including a movable contact and acompanion contact, a contact carrier movable between open and closedpositions, an actuator pivoted to said contact carrier, an overcurrentlatch for said actuator pivoted to said contact carrier, operating meansfor said actuator, said carrier, said latch, and said movable contact,and resilient means for providing contact pressure, said movable contactbeing fixed to said latch, and the pressure of said companion contactagainst said movable contact being directed along a line extendingsubstantially from the pivotal axis of said latch, and electromagneticmeans co-operating with said latch for effecting releasing deflectionthereof.

5. A circuit breaker including a movable contact and a companioncontact, a contact carrier movable between open and closed positions, anactuator pivoted to said contact carrier, an overcurrent latch for saidactuator pivoted to said contact carrier, operating means for saidactuator, said carrier, said latch, and said movable contact, andresilient means for providing contact pressure, said movable contactbeing fixed to said latch and con stituting a combined latch-and-contactunit, means biasing the combined unit in its resetting direction onlyWhile the contacts are apart, and magnetic means energized by currentthrough the circuit breaker and co-operating with said combined unit ineffecting tripping deflection of the latch.

6. A circuit breaker including a contact carrier, a contact-and-latchunit pivoted to said carrier and including a movable contact and furtherincluding an overcurrent latch, an actuator co-operable with said latchand with said carrier, actuating means for driving said actuator forclosing operation of said carrier subject to the control of said latch,a companion contact engageable by said movable contact, an openingspring acting on said carrier for driving the carrier and the movablecontact therewith in the contact-opening direction, a stop for saidcombined unit interposed in the opening path thereof and arranged todrive a portion of said unit against a portion of said carrier, therebyto establish a reset relationship between said latch and said actuator,and electromagnetic means arranged to effect mutual separating movementof said portions and thereby to effect tripping deflection of saidlatch'free of restraint by latch-restoring spring bias.

7. A circuit breaker including a movable contact and a companioncontact, a contact carrier having a supporting pivot between its ends,an actuator pivoted to one end of the contact carrier, overload releasemeans including a current-responsive bimetal latch normally latchingsaid actuator when the circuit breaker is closed, a driving togglearticulated to said actuator and including an operating handle fordriving and locking the contact-carrying arm closed, and an openingspring biasing said contact-carrying arrn open, said movable contact andsaid bimetal latch being united and being pivoted as a unit to saidcarrier, and said carrier and said unit having co-operating stopportions for arresting said unit with said latch in the path of saidactuator, and means biasing said unit in the direction to effect mutualcooperation of said stop portions at least when the circuit breaker isopen.

8. A circuit breaker including a movable contac and a companion contact,a contact carrier movable between open and closed positions, areleasable member pivoted to said contact carrier, a bimetal latch forsaid releasable member pivoted to said contact carrier, operating meansfor said carrier and said movable contact to close the contacts, saidmovable contact being fixed to said bimetal latch as a unitary pivotedelement, and cooperating stops on said carrier and said unitary pivotedelement, said stops forming a reaction point that acts with the pivot ofthe pivoted element to fix one end of the bimetal latch in position toeifect deflection of the latch end of the bimetal latch when heatingoccurs.

9. A circuit breaker including apivoted contact carrier, a releasableelement pivoted to the carrier, a contact-andlatch unit pivoted to saidcarrier and including a movable contact and an overcurrent latchco-operable with said releasable element, a companion contact engageableby said movable contact, and an opening spring acting on said carrierand reacting at a point remote from said overcurrent latch for drivingthe carrier and the movable contact therewith in the contact-openingdirection.

10. A circuit breaker including an enclosing casing of insulation, amovable contact and a companion contact, an elongated carrier for saidmovable contact, a pivot in the casing supporting said contact-carrierbetween the 50 2,887,548

ends thereof, a releasable member pivoted to one end of thecontactcarrier, overload release means including a bimetallic latchnormally latching said releasable member when the circuit breaker isclosed, said movable contact and said latch being united and beingpivoted as a unit to said carrier, said carrier and said unit havingcooperating stop portions coacting with the pivot of the pivoted unit torestrain one end of the pivoted unit in one direction, to provide forlatch releasing deflection of the other end of the bimetallic latch whenheated, and electromagnetic release means acting on said contact--and-latch unit about the pivot thereof, said stop means including abendable adjusting constriction to calibrate the magnetic trippingsensitivity and said contact carrierincluding a bendable adjustingconstriction for adjusting the extent of latch engagement of saidreleasable member with respect to said bimetallic latch and thereby tocalibrate the thermal tripping sensitivity.

11. A circuit breaker including a movable contact and a companioncontact, a contact carrier movable between open and closed positions, anactuator ivotedto said contact carrier, an overcurrent latch for saidactuator pivoted to said contact carrier, operating means for saidactuator, said carrier, said latch and said movable contact for drivingsaid contact carrier into its closed position, saidmovable contact andsaid latch being fixed to each other so as to constitute a combinedunit, the pressure of said companion contact against said movablecontact being directed along a line substantially through the pivotalaxis of said latch, said-combined unit and said contact carrier havingmutually cooperating stops in the reset condition of the circuitbreaker, means biasing said unit in the direction to effect cooperationof said stops with each other at least in the open condition of thecircuit breaker so that said latch may be arrested in an initial resetrelationship with said actuator, and electromagnetic means cooperatingwith said latch and energized by current through'the circuit breaker foreffecting pivotal movement of said combined unit in the direction toeffect release movement of said latch out'of engagement with saidactuator.

References Cited in the file of this patent UNITED STATES PATENTS2,696,540 Christensen Dec. 7, 1954 2,806,103 Gelzheiser Sept. 10, 19572,842,635 Cole July 8, 1958 2,876,308 Christensen Mar. 3, 1959Middendorf May 19, 1959

9. A CIRCUIT BREAKER INCLUDING A PIVOTED CONTACT CARRIER, A RELEASABLEELEMENT PIVOTED TO THE CARRIER, A CONTACT-ANDLATCH UNIT PIVOTED TO SAIDCARRIER AND INCLUDING A MOVABLE CONTACT AND AN OVERCURRENT LATCHCO-OPERABLE WITH SAID RELEASABLE ELEMENT, A COMPANION CONTACT ENGAGEABLEBY SAID MOVABLE CONTACT, AND AN OPENING SPRING ACTING ON SAID CARRIERAND REACTING AT A POINT REMOTE FROM SAID OVERCURRENT LATCH FOR DRIVINGTHE CARRIER AND THE MOVABLE CONTACT THEREWITH IN THE CONTACT-OPENINGDIRECTION.